In wireless telecommunication networks, Long-Term Evolution, or “LTE,” is defined as a standard for wireless communication of high-speed data for mobile phones and data terminals. The LTE standard is developed by the Third Generation Partnership Project (“3GPP”). An exemplary LTE access network is a wireless network of base stations, or evolved NodeBs (“eNBs”), that are interconnected without a centralized intelligent controller. The LTE standard has been described as a natural upgrade path for carriers using prior generation networks or “legacy” protocols, such as Global System for Mobile Communications/Universal Mobile Telecommunications System (“GSM/UMTS”) protocols and Code Division Multiple Access (“CDMA”) 2000 1× (e.g., 1×RTT or simply “1×”) wireless communication protocols. Each of these different types of networks and protocols may be termed radio access technologies (“RATs”).
Through the usage of an all-Internet Protocol (“IP”) network, the LTE standard supports only packet switching (“PS”) data transmissions. Similar to many other protocols, an IP network breaks data into blocks and wraps the blocks into structures called packets. Each packet contains, along with the data load, information about the IP address of the source and the destination nodes, sequence numbers, control information, etc. In a circuit switched (“CS”) network, the communication channel remains open and in use throughout the duration of the call and the call data is transmitted all at once without being broken into blocks.
Mobile phones on older RATs (e.g., GSM, UMTS and CDMA2000) have provided voice call services over a switched-circuit-style network. However, carriers adopting the LTE standard have re-engineered their voice call network to exchange data over an IP packet-switched network, such as Voice over LTE (“VoLTE”), circuit-switched fallback (“CSFB”), and simultaneous voice and LTE (“SVLTE”). For instance, the VoLTE approach uses an IP multimedia subsystem (“IMS”) network having specific profiles for control and media planes of voice service on LTE. The IMS may be defined as an architectural framework for delivering IP multimedia services. IMS was originally designed by the 3GPP as a means for evolving mobile networks beyond GSM and to deliver Internet services over General Packet Radio Service (“GPRS”).